(1) This invention relates to a novel optical active compound and a liquid crystal composition comprising this optical active compound.
(2) Description of the Related Art
Liquid crystals currently used in a liquid crystal display (LCD) are classified into the nematic phase, and since they are of the light-receiving type, they are characterized in that there is no eye fatigue therefrom and the power consumption is very small. Nevertheless, these liquid crystals have problems in that the response speed is low and the view angle of the display is narrow.
Display devices and printer heads using a ferroelectric liquid crystal having advantageous characteristics similar to those of the nematic liquid crystal such as the property of not fatiguing eyes and the small power consumption and also having high response speed and high contrast characteristics comparable to those of a light-emitting type display element has been investigated.
The discovery of the ferroelectric liquid crystal were reported for the first time by R. B. Meyer et al [J. Physique, 36, L-69 (1975]. This ferroelectric liquid crystal is classified into the one exhibiting chiral smectic C phase (hereinafter referred to as "Sm*C phase"), and a typical instance of the ferroelectric liquid crystal is p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate (hereinafter referred to as "DOBAMBC") represented by the following formula ##STR2##
In DOBAMBC and most of the ferroelectric liquid crystals proposed hereafter, the range of temperatures showing the ferroelectric property (the range of temperatures where the Sm*C phase is present) is very narrow, and these liquid crystal materials cannot practically be used alone. Therefore, attempts have been made to expand the range of temperatures showing the Sm*C phase to the lower and higher temperature sides, taking room temperature as the center, by mixing a variety of ferroelectric liquid crystals. A ferroelectric liquid crystal having a larger spontaneous polarization than heretofore proposed ferroelectric liquid crystals is desired for a printer head for which a very short response time is required.
Nevertheless, in the case of mixtures of ferroelectric liquid crystals having an Sm*C phase, the kinds of compounds (liquid crystals) to be mixed are limited, and a liquid crystal mixture having satisfactory performances is difficult to obtain at the present. Moreover, a compound having a Schiff base, such as DOBAMBC, has a poor light stability and is readily colored.